<template>
		<ul class="list">
			<li class="item" v-for="item of letters" :key="item" @click="handleLetterClick"
      @touchstart.prevent="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      :ref="item"
      >{{item}}</li>

		</ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
	  cities: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
	  handleLetterClick (e) {
      this.$emit('change',e.target.innerText)
	  },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if(this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
         const startY = this.$refs['A'][0].offsetTop
         const touchY = e.touches[0].clientY - 79
         const index = Math.floor((touchY - this.startY) / 20)
          if(index >= 0 && index < this.letters.length){
            this.$emit('change', this.letters[index])
          }
        },8)

      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list
  display flex
  flex-direction column
  justify-content center
  position absolute
  right 0
  top 1.58rem
  bottom 0
  width .4rem
.item
  line-height .4rem
  text-align center
  color $bgColor
</style>
